The present invention relates to a stator core structure for dynamoelectric machine, and particularly for an alternator supplying alternating current power to a load distribution system for one or more loads.
Dynamoelectric machines conventionally include an annular stator within which a rotating rotor is rotatably mounted. Engine driven alternators are used for generating alternating current powers in various applications are one example of such machines. Alternators are available for example for providing three phase alternating current at 240/480 volts. The alternator is generally a rotating field construction, with a three phase output winding wound within an annular stationary stator. Conventionally, the stator is formed as a round cylinderical member. The stator is fixedly and rigidly mounted with a tubular mounting frame. The heat generated by the relatively large currents in the windings require forced cooling of the stator to prevent damages to the windings and stator core structures. In open ventilated motors having forced cooling, suitable supporting spacers are circumferentially located about the stator core to space the frame outwardly and define cooling passageways between the outer tubular frame and the exterior surface of the stator core. An appropriate fan unit is coupled to the alternator shaft and is driven therewith to develop an appropriate forced air stream through the alternator and particularly over the stator core to continuously cool the alternator during operation thereof.
Totally enclosed alternators and other dynamoelectric machines are also produced without the internal passageways. In such machines, a finned frame or some other cooling means may be provided. A further highly significant consideration in the construction of dynamoelectric machines is the optimizing of the magnetic material in the core so as to produce an efficient magnetic circuit for the magnetic fields. Thus, cooling and mounting openings in the core tend to effect the path for the fields, and may generally change the path in such a manner as to adversely effect the system.
Although such alternators have been constructed for many years and have produced commercially satisfactory operations, the construction of the core and the assembly of the various spacer and frame components into a final assembly is reasonably costly.
The stators are laminated structures formed of round laminations. The laminations are stamped from a flat strip stock of appropriate magnetic material. There is also a significant material waste as the result of the round configuration with the typical commercial production.
Various alternate constructions have been suggested wherein a substantially square lamination is used with the corners specially shaped for clamping of the stack of laminations together and for mounting of the core to a suitable frame structure when the square stator core is mounted in an annular encircling frame, cooling passageways are formed on the four sides of the core. Such a structure for example is shown in U.S. Pat. No. 2,508,207 which issued on May 16, 1950.
A further modification to the use of a relatively square lamination is disclosed in U.S. Pat. No. 2,818,515 which issued on Dec. 31, 1957. The lamination is formed with a special outer edge configuration defining outward projection from an annular continuous portion including the stator teeth and slot. The laminations are assembled into groups of laminations and the groups are rotated relative to each other to form a stator with circumferential projections and cast within an encircling frame structure. The offsetting of the several groups and casting within the frame structure produces a series of tortuous paths about the projections and thus between the annular portion and the outer cast frame. Although such structure has certain advantages from the standpoint of manufacture, the casting of a frame is not considered a preferred fabrication procedure and the grouped laminating form establishes the airflow path generally in a tortuous path with sharp turns which may restrict rapid cooling of the alternator. Further. The flux pattern and movement within the core structure and particularly the outer most portions thereof is erratic and the extended portions would not appear to significantly contribute to the effective and efficient operation or magnetic functioning of the alternator. Thus, the flux paths within the stator core do not provide a smooth continuous magnetic path with minimum significant air gaps. The stator structure shown in U.S. Pat. No. 2,818,515 also includes the stator stacked between the pressure rings and having rods or iron anchors passing through the grooves formed by grouped laminations and forming an integrated part of the pressure rings and the frame to hold the stacked lamination together as shown in such patent.
There is a need for a laminated stator core structure which can be directly assembled with a tubular cylindrical frame, with an optimum flux distribution within the core and in selected designs with appropriate internal mounting and cooling passages.